Crack propagation in concrete at very early ages

Abstract

Surface defects and cracks in early-age concrete slabs have been observed to propagate under adverse conditions, impairing the performance and service life of these structures. However, the underlying mechanism of this form of crack propagation has remained largely unexplained, with very limited literature available. In this paper, simple yet sufficiently rigorous theoretical analyses of crack propagation in early-age concrete slabs, based on combined geotechnical engineering and fracture mechanics models, are presented. The results obtained clearly show how surface cracks can become unstable and propagate further, and either become stable again or develop through the full depth of the slab. They also convincingly demonstrate the roles of surface cracks and defects, pore moisture suctions and exposure conditions in this process. Importantly, the critical role of good construction practices in minimising this form of cracking is highlighted. These include proper compaction and effective curing as well as timely and adequate saw-cutting.